Various displacement sensors for detecting a bending amount or the like of a subject by using a sheet-shaped member having piezoelectricity are devised. For example, Patent Literature 1 describes a sensor for detecting movement of a columnar projection which moves in the vertical directions by pulsation, using polyvinylidene fluoride (hereinbelow, called PVDF).
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2000-41960